The present invention relates to a method of fabricating ultra-fine cermet alloys with a homogenous solid solution grain structure. More particularly, the invention relates to a method of fabricating an ultra-fine TiC-base cermet alloy with a homogenous solid solution grain structure that does not comprise a core-rim structure in the carbide grain.
In general, the ultra-fine TiC-base cermet alloys are used as cutting tools for the finishing works of steel and cast iron due to their high hardness and abrasion resistance characteristics.
The sintered body of a TiC-base cermet alloy comprises a distinctive dual structure in its carbide grains. This dual structure which is known as the core-rim structure comprises a center region (core) in which the main component includes TiC or TiCN, and a outer (peripheral) second region (rim) which surrounds the core and is mainly a carbide of solid solution such as (Ti, TM)C or (Ti, TM) (C, N), (See, FIG. 8: In reference to Hans-Olof Andrn, “Microstructures of cemented carbides,” Materials and Design, 22, pp491–498 (2002)).
The rim region surrounding the core is also known to form an end-product in the type of solid solution that precipitates on the surface of TiC or TiCN grains as a result of grain growth process in a Ni-rich liquid during liquid phase sintering process (In reference to T. Yamamoto, A. Jaroenworaluck, Y. Ikuhara and T. Sakuma, “Nano-probe analysis of core-rim structure of carbides in TiC-20 wt % Mo2C-20 wt % Ni cermet, “Journal of Materials Research, 14, (1999), pp4129–4131).
The reason for this formation is not contributed to thermodynamically equilibrium structure but more to a kinetic reason (In reference to J. H. shim, C. S. Oh and D. N. Lee, “A thermodynamic evaluation of the Ti—Mo—C system,” Metallurgical and Materials Transaction B, 27B, (1996), pp955–996).
TiC-base cermet alloy with the previously mentioned core-rim structure is not representing the physical property of carbides of uniform grain structure that composition allows but showing the physical property that originates from the dual structure of carbide grains. This also has some drawbacks of deteriorating the physical property of the sintering body.
Accordingly, in perspective of the composition, the cermet with a uniform microstructure could represent a different physical property with respect to that of the existing cermet.
To date, however, no fabrication method of TiC-base cermet alloys with the core-rim structure were able to overcome the limit of kinectic determination.
One of the big emerging technologies in the area of cutting tool material development is improving the hardness and toughness of cutting materials by reducing the size of carbide grains from a few micrometers to several sub-micrometers.
The fabrication methods of ultra-fine grain cutting tool materials which are known to date all involves sintering of carbides powder with a diameter less than 100 nm (nanometer) that is fabricated through a gas phase or solid state reaction.
However, the gas phase or solid state reaction method is inappropriate for massive manufacturing of carbide nano-powders, because the carbide nano-powders obtained from such methods could easily be oxidized when exposed to the atmosphere.